Birei Okami Mie

Based on the erotic game by Lune.

A widow and her daughter own a small restaurant and a young man helps them in the kitchen. The young lady had always loved him and finally confess her love to him and both become lovers but one day she realizes that her mother is lonely and sad because of her late husband so she comes up with a plan where the three of them can be happy together.

(Source: Anime News Network)